On May 30th 1992, the US Postal Service released a 29 cents stamp
called "The Alaska Highway 50th Anniversary Stamp". Could you please
tell me who did the art work for this stamp. Thanks.

Dear cytology,

The artwork for that commemorative 29 cents stamp was done by Brian
Birdsall:

"This design is one of many proposals done by Anchorage artist Brian
Birdsall for the USPS and is based on a 1942 Army photo in the Library
of Congress. The truck is a Dodge 4x4 quarter ton carryall."

Source:
The Alaska Poster Company: Alaska Events on Stamps
http://www.alaskapostercompany.com/AKevents.html

You may want to follow this link to view an enlarged image of the
stamp:
http://www.alaskapostercompany.com/2635.jpg
Source: The Alaska Poster Company

Search terms used:
stamp "alaska highway" 1992 "50th" "postal service"
://www.google.de/search?hl=de&ie=UTF-8&oe=UTF-8&newwindow=1&q=stamp+%22alaska+highway%22+1992+%2250th%22+%22postal+service%22&meta=

Hope this answers your question!
Best regards,
Scriptor